DZone Snippets: Hello's Code Snippets

Calculate Eigenvalues of a given matrix m.

hello (hello) — Fri, 27 May 2005 01:19:52 GMT



> sm <- eigen(m, sym=TRUE)

> V <- sm$vectors

> t(V) %*% V

> V %*% diag(sm$values) %*% t(V)

Delete particular rows from matrix.

hello (hello) — Fri, 27 May 2005 01:16:32 GMT



> x <- matrix(1:10,,2)

> x[x[,1]%in%c(2,3),]

> x[!x[,1]%in%c(2,3),]

from Peter Malewski or from Peter Dalgaard:



> mat[!(mat$first %in% 713:715),]

Create a multidimensional matrix.

hello (hello) — Fri, 27 May 2005 01:04:30 GMT

Brian Ripley said:



> my.array<-array(0,dim=c(10,5,6,8))

will give you a 4-dimensional 10 x 5 x 6 x 8 array.

Or



> array.test <- array(1:64,c(4,4,4))

> array.test[1,1,1]

> 1

> array.test[4,4,4]

> 64

Create an identity matrix.

hello (hello) — Fri, 27 May 2005 01:02:41 GMT



> diag(n)

Or the long way:



> n<-c(5)

> I <- matrix(0,nrow=n,ncol=n)

> I[row(I)==col(I)] <- 1

Create a vector, append values.

hello (hello) — Fri, 27 May 2005 00:59:35 GMT

To create a mathematical vector, you can just initialize a column of numbers with c(). As long as all of your input is of the same type, you don't hit any snags. Note the is.vector() function will say this is a vector:



> v <- c(1, 2, 3) 

> is.vector(v)

Remove a trailing pathname component, leaving the head

hello (hello) — Fri, 27 May 2005 00:57:15 GMT



  $ echo =ls(:h)

  /bin

Hello World - C

hello (hello) — Fri, 27 May 2005 00:44:45 GMT



#include 



main()

{

  for(;;)

      { 

          printf ("Hello World!\n");

      }

}